chat_stream() logs spurious warning "Failed to parse SSE data field as JSON" for [DONE] stream terminator

[Undiluted7027]

SDK Version (required)
5.20.5

Describe the bug
When using ClientV2.chat_stream(), a warning is logged at the end of every successful stream:

Failed to parse SSE data field as JSON: Expecting value: line 1 column 2 (char 1), data: [DONE]

The Cohere API sends [DONE] as the final SSE data value to signal end-of-stream. In v2/raw_client.py, _iter() already handles None as a terminator:

  if _sse.data == None:
      return

But [DONE] falls through to parse_sse_obj(), which tries json.loads("[DONE]"), fails, and logs the warning. After that, parse_obj_as(V2ChatStreamResponse, sse_event) raises a Pydantic ValueError, which is caught by the outer except and silently skipped. So the stream completes correctly and the warning is purely spurious.

Steps to reproduce:

import logging

import cohere

# Enable all logging so the spurious warning is visible
logging.basicConfig(level=logging.DEBUG)

co = cohere.ClientV2()

print("Streaming response:")
for event in co.chat_stream(
    model="command-r7b-12-2024",
    messages=[{"role": "user", "content": "Who created you?"}],
):
    event_type = getattr(event, "type", None)
    if event_type == "content-delta":
        text = (
            event.delta.message.content.text
            if event.delta and event.delta.message and event.delta.message.content
            else ""
        )
        print(text, end="", flush=True)

print("\nDone.")

A fix in v2/raw_client.py could be:

if _sse.data in (None, "[DONE]"):
      return